Revealing contour integration-related ERPs through temporal separation from early visual evoked potentials

Contour integration has been proposed to involve coordinated processing across hierarchical cortical regions. Previous ERP studies have focused primarily on time windows around 200 ms post-contour onset, identifying the occipital N200 and N2pc, which are primarily responsible for visual awareness of integrated shapes and its reliance on spatial attention, respectively. However, findings regarding ERPs at earlier and later stages, as well as how contour properties modulate ERPs related to contour integration, remain unclear. This gap largely stems from traditional paradigms presenting contours at trial onset, confounding early visual evocation with contour integration. To resolve this, we employed a paradigm that temporally dissociates the two processes. By varying contour fidelity, we identified two additional components alongside the occipital N200 and N2pc: an early effect (~100 ms) reflecting feature binding and a late P3b component reflecting task-related effort. Furthermore, the occipital N200 was differentially modulated by contour fidelity and detectability: reducing fidelity through misalignment of contour components decreased its amplitude without affecting latency, whereas reducing detectability through oblique orientation increased latency without affecting amplitude. These findings suggest that the occipital N200 reflects recurrent shape processing, a crucial step in which attended, bound features are integrated into a coherent visual representation that enters conscious awareness, shedding light on how hierarchical processes cooperate dynamically to integrate local elements into a global percept.